Process and materials for inducing alignment of liquid crystals and liquid crystal optical elements

ABSTRACT

The present invention provides novel polyamic acids and polyimide optical alignment layers for inducing alignment of a liquid crystal medium. The novel compositions comprise crosslinking diamines containing a C 3 -C 22  linear or branched hydrocarbon chains containing 1 to 4 carbon-carbon double bonds. The invention further describes liquid crystal displays comprising the novel polyimide optical alignment layers.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation-in-Part of application U.S. Ser. No.09/221,295, filed on Dec. 23, 1998, now U.S. Pat. No. 6,103,322.

This invention was made with United States Government support underAgreement No. MDA972-93-2-0014 awarded by ARPA. The United StatesGovernment has certain rights in the invention.

BACKGROUND OF INVENTION

The present invention relates to materials for aligning liquid crystals,and liquid crystal optical elements.

Current liquid crystal display elements include a product that utilize atwisted nematic mode, i.e. having a structure wherein the aligningdirection of nematic liquid crystal molecules is twisted by 90° betweena pair of upper and lower electrode substrates, a product utilizing asupertwisted nematic mode, utilizing a birefringent effect, i.e. havinga structure wherein the aligning direction of nematic liquid crystalmolecules is twisted by 180° to 300°, an in-plane-switching mode whereinboth electrodes controlling the liquid crystal alignment are present onone substrate and the direction of the liquid crystal orientation in theplane of the substrate changes upon application of an electric field,and a product utilizing a ferroelectric liquid crystal substance or anantiferroelectric liquid crystal substance. Common to each of theseproducts is a liquid crystal layer disposed between a pair of substratescoated with a polymeric alignment layer. The polymeric alignment layercontrols the direction of alignment of the liquid crystal medium in theabsence of an electric field. Usually the direction of alignment of theliquid crystal medium is established in a mechanical buffing processwherein the polymer layer is buffed with a cloth or other fiberousmaterial. The liquid crystal medium contacting the buffed surfacetypically aligns parallel to the mechanical buffing direction.Alternatively, an alignment layer comprising anisotropically absorbingmolecules can be exposed to polarized light to align a liquid crystalmedium as disclosed in U.S. Pat. Nos. 5,032,009 and 4,974,941 “Processof Aligning and Realigning Liquid Crystal Media” which are herebyincorporated by reference.

The process for aligning liquid crystal media with polarized light canbe a noncontact method of alignment that has the potential to reducedust and static charge buildup on alignment layers. Other advantages ofthe optical alignment process include high resolution control ofalignment direction and high quality of alignment.

Requirements of optical alignment layers for liquid crystal displaysinclude low energy threshold for alignment, transparency to visiblelight (no color), good dielectric properties and voltage holding ratios,long-term thermal and optical stability and in many applications acontrolled uniform pre-tilt angle. Most liquid crystal devices,including displays, have a finite pre-tilt angle, controlled, forinstance, by the mechanical buffing of selected polymeric alignmentlayers. The liquid crystal molecules in contact with such a layer alignparallel to the buffing direction, but are not exactly parallel to thesubstrate. The liquid crystal molecules are slightly tilted from thesubstrate, for instance by about 2-15 degrees. For optimum performancein most display applications a finite and uniform pre-tilt angle of theliquid crystal is desirable.

Continuing effort has been directed to the development of processes andcompositions for optical alignment of liquid crystals and liquid crystaldisplays. Through diligent effort and intensive experiments we havefound that the alignment quality and electrical properties, specificallythe voltage holding ratio, of polyimide alignment layers derived frompolyamic acids containing the novel crosslinking diamines disclosedherein are significantly improved over those lacking such crosslinkingcapability.

SUMMARY OF INVENTION

The present invention provides a process for preparing an opticalalignment layer for aligning liquid crystals comprising: preparing alayer of polymer selected from the group consisting of polyamic acid,polyamide ester and polyimide, comprising anisotropically absorbingmolecules, on a substrate; exposing said layer to polarized light; thepolarized light having a wavelength within the absorption band of saidanisotropically absorbing molecules; wherein the resulting exposedanisotropically absorbing molecules induce alignment of a liquid crystalmedium at an angle with respect to the major axis of the polarization ofthe incident light and along the surface of the optical alignment layer;wherein the polymer is further characterized in having side chainsselected from the group of C₃-C₂₂ linear and branched hydrocarbon andpartially fluorinated hydrocarbon chains, optionally substituted by oneto two heteroatoms selected from the group consisting of N, S, O andhaving one to four carbon-carbon double bonds.

Further embodiments of the invention are polymers including polyimides,polyamic acids and esters thereof, characterized in that they compriseidentical or different repeat units selected from one or more of theformula

wherein B is hydrogen or a monovalent organic group derived from analcohol after formal removal of the hydroxyl group, M is a tetravalentorganic radical of a tetracarboxylic acid anhydride after formal removalof the two —CO—O—CO— groups, the four valencies of which are distributedbetween four different carbon atoms of the radical; A is a trivalentunsubstituted or optionally fluoro-, chloro-, cyano-, alkyl-, alkoxy-,fluoroalkyl- or fluoroalkoxy- substituted aromatic or alicyclic radical;Y is selected from the group of C₃-C₂₂ linear and branched hydrocarbonand partially fluorinated hydrocarbon chains, optionally substituted byone to two heteroatoms selected from the group of N, S, O and having oneto four carbon-carbon double bonds.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a system that can be used to expose optical alignmentlayers to ultraviolet light.

FIG. 2 is a cross-sectional view of a general liquid crystal displayelement of the present invention.

DETAILED DESCRIPTION

As used herein, the term “alignment layer” is the layer of material onthe surface of a substrate that controls the alignment of a liquidcrystal layer in the absence of an external field. A “conventionalalignment layer” herein refers to an alignment layer that will onlyalign a liquid crystal layer via processing other than optical means.For example, mechanically buffed polyimides, evaporated silicon dioxide,and Langmuir-Blodgett films, have all been shown to align liquidcrystals.

“Optical alignment layer” herein refers to an alignment layer thatcontains anisotropically absorbing molecules that will induce alignmentof liquid crystals after exposure with polarized light. The opticalalignment layer can be an isotropic medium or have some degree ofanisotropy before optical alignment. Optical alignment layers may beprocessed by conventional means, such as mechanical rubbing, prior to orafter exposure to polarized light. The anisotropically absorbingmolecules of the optical alignment layers exhibit absorption propertieswith different values when measured along axes in different directions.The anisotropic absorbing molecules exhibit absorption bands between 150nm and about 2000 nm. Most preferable optical alignment layers for thepresent invention have absorbance maxima of about from 150 to 400 nm andespecially about from 300 to 400 nm.

Anisotropically absorbing molecules that can be used in opticalalignment layers and various methods for forming optical alignmentlayers are discussed in U.S. Pat. No. 5,731,405 entitled “Process andMaterials for Inducing Pre-tilt in Liquid Crystals and Liquid CrystalDisplays, hereby incorporated by reference.

Polymers especially useful and preferred as optical alignment layers arepolyimides. Polyimides are known for their excellent thermal andelectrical stability properties and these properties are useful inoptical alignment layers for liquid crystal displays. The preparation ofpolyimides is described in “Polyimides”, D. Wilson, H. D. Stenzenberger,and P. M. Hergenrother Eds., Chapman and Hall, New York (1990).Typically polyimides are prepared by the condensation of one equivalentof a diamine with one equivalent of a dianhydride in a polar solvent togive a poly(amic acid) prepolymer intermediate. Alternatively copolymerpolyimides are prepared by the condensation of one or more diamines withone or more dianhydrides to give a copolyamic acid.

An alternative intermediate to polyimides are polyamic esters that canbe made by esterification of polyamic acids with alcohols. The polyamicesters undergo thermal imidization to form polyimides.

Thus, poly(amic acids) and poly(amic esters) are considered to beclosely related precursors to polyimides of the invention. Therefore,they are considered further embodiments of this invention. Furthermore,preimidized polyimides derived from chemical or thermal imidization ofpoly(amide acids) or poly(amide esters) are also considered anembodiment of the invention.

The polyamic acid is typically formulated to give a 1 to 30 wt %solution. The condensation reaction is usually performed between roomtemperature and 150° C. The prepolymer solution is coated onto a desiredsubstrate and thermally cured at between 180 and 300° C. to complete theimidization process. Alternatively, the poly(amic acid) prepolymer ischemically imidized by addition of a dehydrating agent to form apolyimide polymer.

In preparing polyamic acids for optical alignment layers the molar ratioof diamine to dianhydride usually is 1:1, but can vary between 0.8:1 to1.2:1. The preferred ratio of diamine to dianhydride is between 0.9:1and 1.1:1.

Novel polymers of the invention include polyimides, polyamic acids andesters thereof, characterized in that they comprise identical ordifferent repeat units selected from one or more of the formula

wherein B is hydrogen or a monovalent organic group derived from analcohol after formal removal of the hydroxyl group, M is a tetravalentorganic radical of a tetracarboxylic acid dianhydride after formalremoval of the two —CO—O—CO— groups, the four valencies of which aredistributed between four different carbon atoms of the radical; A is atrivalent unsubstituted or optionally fluoro-, chloro-, cyano-, alkyl-,alkoxy-, fluoroalkyl- or fluoroalkoxy-substituted aromatic or alicyclicradical; Y is selected from the group of C₃-C₂₂ linear and branchedhydrocarbon and partially fluorinated hydrocarbon chains, optionallysubstituted by one to two heteroatoms selected from the group of N, S, Oand having one to four carbon-carbon double bonds. Preferred arepolymers wherein the double bond(s) is (are) unconjugated to any otherHI system.

The term “optionally substituted by one to two heteroatoms selected fromthe group of N, S, O” means that one to two carbon atoms in thehydrocarbon and partially fluorinated hydrocarbon chain can be formallyreplaced by oxygen, nitrogen or sulfur.

Preferred polymers are those wherein Y is —X—R₁, wherein R₁ is selectedfrom the group of C₃-C₂₀ linear and branched hydrocarbon chains havingone to four carbon-carbon double bonds and X is a divalent moietyselected from the group —O—, —S— and —NR—, wherein R is selected,independently, from H, R₁, and C₁ to C₄ hydrocarbon chain. Morepreferred polymers are those wherein A is selected from the groupconsisting of phenyl, napthyl, biphenyl, pyridinyl and pyrimidinylradicals and most preferred polymers are those wherein A is a phenylradical.

Preferred polyimides, polyamic acids and esters thereof compriseidentical or different repeat units selected from one or more of theformula

wherein Ar is a divalent unsubstituted or optionally fluoro-, chloro-,or cyano-substituted aromatic radical, A, Y and B are as defined above,and X₁, Z and m are as defined below. Preferably Ar, within the aryldiketone polymers, is selected from the group consisting of phenyl,biphenyl, pyridinyl, diphenyl ether and napthyl radical.

Most preferred polyamic acids of the invention for inducing alignment ofa liquid crystal medium adjacent to a surface of an optical alignmentlayer comprise polyamic acids of structure I

wherein R₁ is selected from the group of C₃-C₂₀ linear or branchedhydrocarbon chain containing 1 to 4 carbon-carbon double bonds; X is adivalent moiety selected from the group consisting of —O—, —S—, and—NR—, wherein R is selected from the group consisting of H, R₁, andC₁-C₄ hydrocarbon chain; X₁ is independently selected from the groupconsisting of H, Cl, F, and Br; m is 1 or 0; Z is selected from thegroup consisting of —S—, —O—, —SO₂—, —CH₂—, —C(CF₃)₂—, —C(O)—, —CH₂CH₂—,—NR₂— and a covalent bond wherein R₂ is selected from the groupconsisting of H and C₁-C₄ hydrocarbon chain; and the carboxylic acidgroups are ortho to the amide linkages. Coatings of these polyamicacids, upon chemical or thermal imidization, give polyimide opticalalignment layers that are useful for aligning liquid crystals. As willbe discussed further below, the novel polyimide optical alignment layersprovide high sensitivity to polarized light and improved electricalproperties over polyimides without crosslinking functionality providedby the polyamic acids of structure I.

Preferred polyamic acids of structure I are those wherein R₁ is

wherein R₃ is selected from the group of H and C₁-C₁₀ hydrocarbon chain;R₄ is selected from the group of R₃ and

n is an integer from 1 to 10 and p is an integer from 0 to 10.

Preferred polyamic acids of the invention are wherein m is 0 and X₁ is Hor Cl. These are derived from 3,3′,4,4′-benzophenonetetracarboxylicdianhydride and 2,2′-dichloro-4,4′,5,5′-benzophenone tetracarboxylicdianhydride. Both materials are colorless, provide reasonable solubilitycharacteristics to the polyamic acids, and provide a photoactive UVchromophore in high concentration.

The benzophenonetetracarboxylic dianhydrides are readily available fromcommercial sources or synthesis. For instance,3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) is availablefrom Aldrich Chemical Co., Inc. (1001 W. St. Paul Ave., Milwaukee, Wis.53233). 2,2′-Dichloro-4,4′,5,5′-benzophenone tetracarboxylic dianhydrideis available from 4-chloro-o-xylene by Friedel-Crafts acylation withoxalyl chloride to give2,2′-dichloro-4,4′,5,5′,-tetramethylbenzophenone, followed by oxidationwith nitric acid and dehydration of the resulting tetracarboxylic acidas described by Falcigno, et al., J. Poly. Sci. 1992, 30, 1433.Synthesis of bis-(dicarboxyphenylketone)aryl dianhydrides, required toprepare the aryl diketone polymers above, are described in J. R. Pratt,et al. (Polymer Engineering and Science, 1989, 29, 63-68), French PatentSpecification No. 1,601,094, and by Sonnenberg in U.S. Pat. No.4,002,645.

Other diaryl ketones dianhydrides that are useful in the process of theinvention, wherein m is 1, are the polycyclic diaryl ketone dianhydridesdescribed by Pfeifer, et al., in U.S. Pat. No. 4,698,295 and herebyincorporated by reference. Another diaryl ketone dianhydride that may beuseful is 5,5′-[carbonylbis(4,1-phenyleneoxy)]bis-1,3-isobenzofuranone,Structure III:

A wide variety of other dianhydrides, of course, may be used in formingcopolyamic acids. Specific examples of other tetracarboxylic dianhydridecomponents include aromatic dianhydrides such as pyromelliticdianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride,1,2,5,6-naphthalenetetracarboxylic dianhydride,1,4,5,8-naphthalenetetracarboxylic dianhydride,3,3′,4,4′-biphenyltetracarboxylic dianhydride,2,3,2′,3′-biphenyltetracarboxylic dianhydride,bis(3,4-dicarboxyphenyl)ether dianhydride,bis(3,4-dicarboxyphenyl)diphenylsulfone dianhydride,bis(3,4-dicarboxyphenyl)methane dianhydride,2,2-bis(3,4-dicarboxyphenyl)propane dianhydride,1,1,1,3,3,3-hexafluoro-2,2-bis(3,4-dicarboxyphenyl)propane dianhydride,bis(3,4-dicarboxyphenyl)dimethylsilane dianhydride,2,3,4,5-pyridinetetracarboxylic dianhydride; alicyclic tetracarboxylicdianhydrides such as 1,2,3,4-butanetetracarboxylic dianhydride,1,2,3,4-cyclobutanetetracarboxylic dianhydride,1,2,3,4-cyclopentanetetracarboxylic dianhydride,1,2,4,5-cyclohexanetetracarboxylic dianhydride,2,3,5-tricarboxycyclopentylacetic acid dianhydride and3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalenesuccinic dianhydride; andtheir acid and acid chloride derivatives.

The novel polyamic acids of the invention require novel crosslinkingdiamines of structure

wherein R₁ is selected from the group of C₃-C₂₀ linear or branchedhydrocarbon chain containing 1 to 4 carbon-carbon double bonds and X isa divalent moiety selected from the group —O—, —S—, and —NR—, wherein Ris selected from H, R₁, and C₁-C₄ hydrocarbon chain. Preferred diaminesare wherein R₁ is a C₁₀-C₂₀ linear or branched hydrocarbon chaincontaining 2 to 4 carbon-carbon double bonds and X is —NR—, wherein R isselected from H, R₁, and C₁-C₄ hydrocarbon.

Specific examples of the novel crosslinking diamines are listed in Table1 and their syntheses are described in the Examples. In general, a widevariety of crosslinking diamines of the invention are readily availableby reaction of a secondary unsaturated amine withfluoro-2,4-dinitrobenzene or 3-fluoro-4-nitroaniline followed byreduction of the nitro groups to the corresponding primary amines. Manysecondary unsaturated amines that would be useful in preparing the novelamines are commecially available including diallyl amine, andN-ethyl-2-methylallylamine. Other secondary unsaturated amines areavailable by synthesis including N-methyl-N-geranylamine,N-methyl-N-citronellylamine N-methyl-N-farnesylamine,N-methyl-N-oleylamine, and N-methyl-N-3-methylbutenamine.

Novel crosslinking diamines containing ether linkages are readilyavailable by alkylation of 2,4-dinitrophenol or 2,5-dinitrophenol withunsaturated alkyl halides followed by reduction of the nitro groups tothe corresponding primary amines. Commecially available unsaturatedalkyl halides useful in preparing the novel amines include5-bromo-1-pentene, 5-bromo-2-methyl-2-pentene, 6-bromo-1-hexene,8-bromo-1-octene, 4-bromo-2-methyl-2-butene, geranyl bromide, famesylbromide, famesyl chloride, and citronellyl bromide. Other alkyl halidesuseful in preparing the novel diamines are available by conversion ofthe corresponding unsaturated alcohols to bromides or chlorides. Usefulalcohols include nerol (cis-3,7-dimethyl-2,6-octadien-1-ol), phytol(3,7,11,15-tetramethyl-2-hexadecen-1-ol), and β-citronellol.

A variety of other diamines may be useful in the preparation of novelcopolyamic acids of the invention including aromatic diamines such as2,5-diaminobenzonitrile, 2-(trifluoromethyl)-1,4-benzenediamine,p-phenylenediamine, 2-chloro-1,4-benzenediamine,2-fluoro-1,4-benzenediamine, m-phenylenediamine, 2,5-diaminotoluene,2,6-diaminotoluene, 4,4′-diaminobiphenyl,3,3′-dimethyl-4,4′-diaminobiphenyl, 3,3′-dimethoxy-4,4′-diaminobiphenyl,diaminodiphenylmethane, diaminodiphenyl ether,2,2-diaminodiphenylpropane, bis(3,5-diethyl-4-aminophenyl)methane,diaminodiphenylsulfone, diaminonaphthalene,1,4-bis(4-aminophenoxy)benzene, 4,4′-diaminobenzophenone,3,4′-diaminobenzophenone, 1,4-bis(4-aminophenyl)benzene,9,10-bis(4-aminophenyl)anthracene, 1,3-bis(4-aminophenoxy)benzene,4,4′-bis(4-aminophenoxy)diphenylsulfone,2,2-bis[4-(4-aminophenoxy)phenyl]propane,2,2-bis(4-aminophenyl)hexafluoropropane and2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane; alicyclic diaminessuch as bis(4-aminocyclohexyl)methane; and aliphatic diamines such astetramethylenediamine and hexamethylene diamine. Further,diaminosiloxanes such as bis(3-aminopropyl)tetramethyldisiloxane may beused. Such diamines may be used alone or in combination as a mixture oftwo or more of them. Preferred diamines for preparing copolyamic acidsare 2,5-diaminobenzonitrile, 2-(trifluoromethyl)-1,4-benzenediamine and1,4-phenylene diamine. Most preferred are 2,5-diaminobenzonitrile and2-(trifluoromethyl)-1,4-benzenediamine.

Preferred copolyamic acids comprise the structure I (above) andadditionally comprise structure II

wherein X₂ is selected from the group H, C₁-C₄ hydrocarbon, —CN, —CF₃,F, Cl, Br, I, —NO₂, —OR₂, —CO₂R₂, and —CO₂N(R₂)₂, wherein R₂ is H or aC₁-C₄ hydrocarbon. A most preferred copolyamic acid is wherein X₁ is H,m is 0, and X₂ is selected from the group —CN and —CF₃.

Table 2 lists several diamines that are used in forming preferredcopolyamic acids of the invention. Amines 15 and 16 in Table 2 exemplifystructural elements that, when incorporated into polyimides, are usefulin inducing pre-tilt properties in optical alignment layers. Typically,a polyamic acid wherein between about 1 to 20 mol % of the aminecomponent comprises monoamine 15, or a combination of monoamine 15 anddiamine 16, when converted to a polyimide optical alignment layer, willexhibit a finite pre-tilt when optically aligned. The pre-tilt istypically higher with polyimides comprising these amines than withpolyimides not comprising one or more of these amines. Examples 28 thru31 demonstrate copolyimides of the invention that also comprise pre-tiltinducing diamines.

Preferably the novel polyamic acids of the invention comprise about from1 to 100 mol % of structure I; more preferably from 5 to 50 mol % ofstructure I; and most preferably from 5 to 25 mol % of structure I. Ahigher mol % of structure I tends to give a higher degree ofcrosslinking and improved electrical properties. However, improvement involtage holding ratio (VHR) and the photosensitivity of the polyimideoptical alignment layer is often observed at relatively low loading ofstructure I in a copolyamic acid.

To prepare the optical alignment layers the poly(amic acid) solutions orpreimidized polyimide solutions are coated onto desired substrates.Coating is usually accomplished with 2 to 30 wt % solids. Anyconventional method may be used to coat the substrates includingbrushing, spraying, spin-casting, meniscus coating, dipping or printing.The preferred techniques for coating substrates demonstrated in theExamples are spinning and printing. However, the optical alignmentmaterials of the invention are not limited to use in printing orspinning processes.

The coated substrates are heated in an oven under an inert atmosphere,for instance nitrogen or argon, at elevated temperature usually notexceeding 300° C. and preferably at or below 180° C. for about from 1 to12 hours, preferably for about 2 hours or less. The heating processremoves the solvent carrier and may be used to further cure the polymer.For instance, the poly(amic) acid films are thermally cured to generatepolyimide films.

The concentration of polymer and choice of solvents can affect theoptical alignment quality, pretilt and VHR. For example, the opticalalignment quality has been observed to improve under the same exposureconditions when the concentration of polymer is decreased in solution.In addition, the choice of solvent and/or co-solvents can also affectthe alignment quality. A correlation between film thickness andalignment quality also is evident. In particular, the optical alignmentquality improves with decreasing thickness. Similarly, VHR increaseswith decreasing film thickness.

The optical alignment layers are exposed to polarized light to inducealignment of liquid crystals. By “polarized light” is meant light thatis elliptically polarized such that the light is more polarized alongone axis (referred to as the major axis) versus the orthogonal axis(referred to as the minor axis). In this invention the polarized lighthas one or more wavelengths of about from 150 to 2000 nm and preferablyof about from 150 and 1600 nm and more preferably about from 150 to 800nm. Most preferably, the polarized light has one or more wavelengths ofabout from 150 to 400 nm, and especially about from 300 to 400 nm. Apreferred source of light is a laser, e.g., an argon, helium neon, orhelium cadmium. Other preferred sources of light are mercury arcdeuterium and quartz tungsten halogen lamps, xenon lamps, microwaveexcited lamps and black lights in combination with a polarizer.Polarizers useful in generating polarized light from nonpolarized lightsources are interference polarizers made from dielectric stacks,absorptive polarizers, diffraction gratings and reflective polarizersbased on Brewster reflection. With lower power lasers or when aligningsmall alignment regions, it may be necessary to focus the light beamonto the optical alignment layer.

By “exposing” is meant that polarized light is applied to the entireoptical alignment layer or to a portion thereof. The light beam may bestationary or rotated. Exposures can be in one step, in bursts, inscanning mode or by other methods. Exposure times vary widely with thematerials used, etc., and can range from less than 1 msec to over anhour. Exposure may be conducted before or after contacting the opticalalignment layer with the liquid crystal medium. Exposing can beaccomplished by linearly polarized light transmitted through at leastone mask having a pattern or with a beam of linearly polarized lightscanned in a pattern. Exposing also may be accomplished usinginterference of coherent optical beams forming patterns, i.e.,alternating dark and bright lines.

Exposure energy requirements vary with the formulation and processing ofthe optical alignment layer prior and during exposure. A preferred rangeof exposure energy is about from 0.001 to 100 J/cm² and most preferredrange of exposure energy is about from 0.001 to 5 J/cm². Lower exposureenergy is most useful in large scale manufacturing of optical alignmentlayers and liquid crystal display elements. Lower exposure energy alsominimizes the risk of damage to other materials on the substrates.

The efficiency of the alignment process, and the exposure energyrequired, may be further impacted by heating, beyond that inherent inthe “exposing” step. Additional heating during the exposing step may beaccomplished by conduction, convection or radiant heating, or byexposure to unpolarized light. Additional heating may increase themobility of the molecules during exposure and improve the alignmentquality of the optical alignment layer. Additional heating is not arequirement of the process of the invention but may give beneficialresults.

The quality of alignment and electrical properties of the liquid crystalcell assembled from exposed substrates can be improved by heating thesubstrates after exposure but prior to assembly of the cell. Thisadditional heating of the substrates is not a requirement of the processbut may give beneficial results.

Exposing also can consist of two or more exposure steps wherein theconditions of each step such as angle of incidence, polarization state,energy density, and wavelength are changed. At least one of the stepsmust consist of exposure with linearly polarized light. Exposures canalso be localized to regions much smaller than the substrate size tosizes comparable to the entire substrate size. A preferred method ofdual exposing comprises a two step process of:

(a) exposing at least one optical alignment layer to polarized light ata normal incidence, and

(b) exposing the optical alignment layer to polarized light at anoblique incidence.

Applying a liquid crystal medium to the optical alignment can beaccomplished by capillary filling of a cell, by casting of a liquidcrystal medium onto an optical alignment layer, by laminating apreformed liquid crystal film onto an optical alignment layer or byother methods. Preferred methods are capillary filling of a cell,injection filling and casting of a liquid crystal medium onto an opticalalignment layer. Optical alignment layers are pre-exposed to polarizedlight or they are exposed after contacting the liquid crystal medium.

A cell can be prepared by using two coated substrates to provide asandwiched layer of liquid crystal medium. The pair of substrates canboth contain optical alignment layers or a conventional alignment layer(e.g., mechanically buffed) can be used as the second alignment layercomprising the same or a different polymer.

As liquid crystal substances used for liquid crystal optical elements,nematic liquid crystal substances, ferroelectric liquid crystalsubstances, etc. are usable. Useful liquid crystals for the inventiondescribed herein include positive dielectric liquid crystals including4-cyano-4′-alkylbiphenyls, 4-cyano-4′-alkyloxybiphenyls,4-alkyl-(4′-cyanophenyl)cyclohexanes,4-alkyl-(4′cyanobiphenyl)cyclohexanes, 4-cyanophenyl-4″alkylbenzoates,4-cyanophenyl-4′alkyloxybenzoates, 4-alkyloxyphenyl-4′cyanobenzoates,4-alkylphenyl-4′alkylbenzoates, 1-(4′-alkylphenyl)-4-cyanopyrimidines,1-(4′-alkyloxyphenyl)-4-cyanopyrimidines and1-(4-cyanophenyl)-4-alkylpyrimidines. Other useful liquid crystals arenew superfluorinated liquid crystals available from EM Industries,(Hawthrone N.Y.) including the commercial materials: ZLI-5079, ZLI-5080,ZLI-5081, ZLI-5092, ZLI-4792, ZLI-1828, MLC-2016, MLC-2019, MLC-6252 andMLC-6043. Other useful nematic materials for practicing the inventioninclude the commercial liquid crystals available from Dinippon Ink andChemicals Co., Ltd, (Tokyo, Japan) including the DLC series: 22111,22112, 22121, 22122, 23070, 23170, 23080, 23180, 42111, 42112, 42121,42122, 43001,43002, 43003, 63001, 63002, 63003, 63004, and 63005.

The invention is not limited to the use of liquid crystals definedabove. One skilled in the art will recognize that the invention will beof value with many diverse liquid crystal structures and formulationscontaining mixtures of liquid crystals.

The exposed optical alignment layer induces alignment of a liquidcrystal medium at an angle with respect to the direction of the linearpolarization of the incident light beam and along the plane of theoptical alignment layer. One skilled in the art will recognize that theprocess allows control of the alignment of a liquid crystal medium inany desired direction within the plane of the optical alignment layer bycontrolling the conditions of the polarized light exposure.

A liquid crystal display element of the invention is composed of anelectrode substrate having at least one polyimide optical alignmentlayer derived from a polyamic acid of Structure I (above), avoltage-impressing means and a liquid crystal material. FIG. 2illustrates a typical liquid crystal display element, comprising atransparent electrode 13 of ITO (indium-tin oxide) or tin oxide on asubstrate 12 and optical alignment layers 14 formed thereon. The opticalalignment layers are exposed to polarized light of a wavelength orwavelengths within the absorption band of the anisotropically absorbingmolecules. A spacer concurrently with a sealing resin 15 is intervenedbetween a pair of optical alignment layers 14. A liquid crystal 16 isapplied by capillary filling of the cell and the cell is sealed toconstruct a liquid crystal display element. Substrate 12 may comprise anovercoat film such as an insulating film, a color filter, a color filterovercoat, a laminated polarizing film etc. These coatings and films areall considered part of the substrate 12. Further, active elements suchas thin film transistors, a nonlinear resistant element, etc. may alsobe formed on the substrate 12. These electrodes, undercoats, overcoats,etc. are conventional constituents for liquid crystal display elementsand are usable in the display elements of this invention. Using the thusformed electrode substrate, a liquid crystal display cell is prepared,and a liquid crystal substance is filled in the space of the cell, toprepare a liquid crystal display element in combination with avoltage-impressing means.

Optical alignment layers of the invention are compatible with all liquidcrystal display modes. A liquid crystal display element of the inventioncan comprise a variety of display configurations including twistednematic, super twisted nematic, in-plane-switching, vertical alignment,active-matrix, cholesteric, polymer dispersed, ferroelectric,anti-ferroelectric and multi-domain liquid crystal displays. Althoughthe display modes demonstrated in this specification are primarilytwisted nematic, the optical alignment layers of the invention are notlimited to use in twisted nematic liquid crystal displays.

Optical alignment layers of the invention are useful in many otherliquid crystal devices other than liquid crystal displays. These includeelectro-optical light modulators, all-optical light modulators, erasableread/write optical data storage media; diffractive optical componentssuch as gratings, beamsplitters, lenses (e.g., Fresnel lenses), passiveimaging systems, Fourier processors, optical disc and radiationcollimators; binary optical devices formed by combining refractive anddiffractive optics including eyeglasses, cameras, night vision goggles,robotic vision and three-dimensional image viewing devices; andholographic devices such as heads-up displays and optical scanners.

Voltage Holding Ratio (VHR) is a critical electrical parameter forliquid crystal displays. VHR is a measure of the LCDs ability to retaina voltage during the time between pixel updates (frame time). The typeof liquid crystal, alignment layers and cell geometry can all affect themeasured VHR value. In the examples to follow, liquid crystal test cellscomprising soda-lime substrates with patterned indium-tin-oxide (ITO)transparent electrodes are described. The overlap of the electrodes wasabout 1 cm² after the test cell was assembled. Approximately 2-3 inchwire leads were attached to the patterned ITO electrodes using anultrasonic solder iron after the test cell is assembled but prior tofiling. The leads were attached to a VHR measurement system (ElsiconVHR-100 Voltage Holding Ratio Measurement System, Wilmington, Delaware)using test clips after the cell was filled and annealed. The VHR for theexamples was measured for a 20 msec frame time, which is typically usedfor measuring VHR. The VHR at room temperature for the various exposureconditions is summarized in Table 3.

The examples of the invention use fluorinated amines 15 and 16 that wereprepared by the following procedures:

A mixture of 4-fluoronitrobenzene (141.1 g), 1H,1H-perfluorooctanol(420.1 g), and potassium hydroxide (79.2 g) in 1-methyl-2-pyrrolidinone(1.0 L) was stirred at room temperature for 16 h under a nitrogenatmosphere. The mixture was extracted from aqueous solution andconcentrated to give 4-(1H,1H-perfluorooctyloxy)nitrobenzene which wasreduced with hydrogen and 5% Pd/C. The product was distilled andrecrystallized to give 4-(1H,1H-perfluorooctyloxy)benzeneamine, 15, ascrystals, mp 49.1-50.2° C.

A mixture of 2,2,3,3,4,4,5,5-octafluoro-1,6-hexanediol (78.63 g, 0.3mol, Aldrich Chemical Co., Milwaukee, Wis.), 1-fluoro-2,4-dinitrobenzene(18.6 g, 0.10 mmol), triethyl amine (42 mL, 0.3 mol) and acetone (100mL) was heated to 80° C. for 1.5 hr. After aqueous workup the excesshexanediol was removed by Kugelrohr distillation and the dimerby-product was removed by crystallization. The mother liquor wasconcentrated to give an orange oil. A portion of the oil (8.5 g) wastreated with tin chloride dihydrate (36.0 g), ethanol (40 mL) and 10 Nhydrochloric acid (30 mL) for 17 h at 35° C. to give the diamine 16.

N-methylgeranylamine used in the examples was prepared by treatment ofgeranyl bromide with 12 fold excess of methylamine in ethanol. Theproduct was isolated by extraction into ethyl ether and distillation.N-methylfamesylamine, N-methylcitronellylamine andN-methyl-3-methyl-3-butenylamine are prepared in a similar manner.N-methyloleylamine was prepared by methylation of the N-oleylacetamidepotassium salt followed by hydrolysis.

TABLE 1 Crosslinking Diamines. Diamine No. Structure 1

2

3

4

5

6

7

8

9

10

11

12

TABLE 2 Amines used to prepare polyamic acids in Example Diamine No.Structure 13

14

15

16

17

TABLE 3 Optical Alignment of Polyimide compositions, ProcessingParameters and Results. Exposure Polyimide Composition Coating LaserExample BDTA + Diamine No. S = spincast scan Lamp Alignment No. (molarratio in copolymers) Wt % P = printing mm/sec J/cm² Quality VHR 13a 13 +1 (0.9:0.1) 4 S 0.75 — ◯+ 0.962 B ″ 4 S 1.5 — ◯+ 0.966 C ″ 4 S 3.0 — ◯+0.931 D ″ 4 S 6.0 — Δ 0.890 E ″ 3 S 6.0 — ◯+ 0.948 F ″ 5 P 3.0 — ◯+0.958 G ″ 5 P 6.0 — ◯ 0.931 H ″ 5 P — 40 Δ++ 0.967 I ″ 5 P — 20 ◯++0.968 J ″ 5 P — 10 ◯ 0.965 14a 13 + 1 (0.8:0.2) 5 S 0.75 — Δ+ 0.979 b ″5 S 1.5 — ◯ 0.964 15a 13 + 1 (1:1) 5 S 0.75 — ×++ 0.985 b ″ 5 S 1.5 — ×0.982 c ″ 5 S 6.0 — × 0.966 d ″ 5 S 10 — × 0.962 16a 1 5 S 0.75 — ×++0.981 b ″ 5 S 1.5 — × 0.981 17a 13 + 2 (0.8:0.2) 5 S 0.75 — Δ++ 0.977 b″ 5 S 1.5 — ◯++ 0.965 18a 13 + 2 (0.9:0.1) 4 S 0.75 — ◯++ 0.956 b ″ 4 S1.5 — ◯+ 0.959 19a 13 + 3 (0.9:0.1) 4 S 0.75 — Δ++ 0.960 b ″ 4 S 1.5 — ◯0.954 c ″ 4 S 4.0 — ◯ 0.877 20a 13 + 4 (0.8:0.2) 4 S 0.75 — ◯+ 0.959 b ″4 S 1.5 — ◯+ 0.967 21a 13 + 5 (0.8:0.2) 4 S 0.75 — ◯ 0.969 b ″ 4 S 1.5 —◯ 0.953 c ″ 4 S 4.0 — Δ++ 0.843 22a 13 + 6 (0.9:0.1) 4 S 0.75 — ◯++0.970 b ″ 4 S 1.5 — ◯++ 0.964 c ″ 4 S 4.0 ◯++ 0.953 23a 13 + 6 (0.8:0.2)4 S 0.75 — ◯ 0.96 b ″ 4 S 1.5 — ◯ 0.97 c ″ 4 S 6.0 — Δ 0.95 24a 14 + 1(0.9:0.1) 5 S 0.75 — ◯++ 0.874 b ″ 5 S 1.5 — ◯++ 0.942 c ″ 5 S 4.0 — ◯+0.836 25a 17 + 1 (0.9:0.1) 3 S 0.75 — ◯+ 0.927 b ″ 3 S 1.5 — Δ 0.863 26a13 3 S 1.5 — Δ++ 0.933 b 13 3 S 3.0 — Δ++ 0.924 27a 14 3.5 S 1.5 — ◯+0.815 b 14 3.5 S 3.0 — Δ+ 0.834 28a 13, 1 + 15 (1.75:0.19:0.1) 4 S 0.75— Δ 0.898 b ″ 4 S 1.5 — ×+ 0.790 29a 13, 4 + 15 (1.75:0.19:0.1) 4 S 0.75— ◯++ 0.904 b ″ 4 S 1.5 — ◯ 0.799 30a 13, 2, 15, + 16 4 S 0.75 — Δ 0.892(0.8:0.1:0.05:0.075) b 13, 2, 15, + 16 4 S 1.5 — ×+ 0.802(0.8:0.1:0.05:0.075) 31a 13, 1, 15 + 16 4 S 0.75 — ◯++ 0.911(0.81:0.1:0.025:0.075) b 13, 1, 15, + 16 4 S 1.5 — ◯++ 0.854(0.81:0.1:0.025:0.075) • Excellent alignment, no flow effects, highuniformity. ◯  Good alignment, low flow effects, uniform. Δ Fairalignment, flow effects, some nonuniformity (mottled or cloudybackground). × Poor alignment, severe flow effects, nonuniform. + Levelsof improvement, Δ < Δ+ < Δ++ < ◯

Examples 1-12 describe the formation of novel crosslinking diamines 1-12of the invention.

EXAMPLE 1

A mixture of 2,4-dinitrofluorobenzene (9.3 g, 50 mmol),1-methylpyrrolidinone (50 mL), diallylamine (5.82 g, 60 mmol) andpotassium carbonate (6.9 g, 50 mmol) was stirred at ambient temperaturefor 1 h. The mixture was poured into water (250 mL) and extracted withethyl ether. The ether extract was washed with 0.5 N hydrochloric acid,water, and saturated brine solution, and dried over magnesium sulfate.Concentration of the extract gave N,N-diallyl-2,4-dinitrobenzeneamine asa yellow oil (14.6 g).

The above yellow oil (14.6 g) was treated with a solution of tin (II)chloride dihydrate (90.0 g, 0.40 mol), 10 N hydrochloric acid (75 mL)and ethanol (250 mL, absolute) at 55-60° C. for 14.5 h. The mixture waspoured into ice water (400 mL) and basified with 20 wt % potassiumhydroxide solution (750 g) chilled to 0° C. The mixture was extractedwith ethyl ether—tetrahydrofuran (4:1, 600 mL), and the combinedextracts washed with deionized water three times, washed with saturatedbrine solution, and dried with magnesium sulfate. The mixture wasconcentrated to a yellow oil that was purified by chromatography onsilica gel and kugelrohr distilled at 115-120° C. (0.1 mm Hg) to giveN,N-diallyl-1,2,4-benzenetriamine, 1, as a yellow oil. ¹H NMR (CDCl₃)6.79 (d, 1H), 6.08 (m, 2H), 5.80 (m, 2H), 5.10 (m, 4H), 3.45 (dt, 4H),4.0 (bs) and 3.5 (bs).

EXAMPLE 2

A mixture of 3-fluoro-4-nitroaniline (1.56 g, 10 mmol),1-methylpyrrolidinone (10 mL), diallylamine (1.94 g, 20 mmol) andpotassium carbonate (1.38 g, 10 mmol) was heated to 115-125° C. for 9.5h. The mixture was diluted with water, and extracted with ethyl ether.The combined extracts were washed with water, washed with saturatedbrine solution, and dried over magnesium sulfate. The extract wasconcentrated to give N,N-diallyl-6-nitro-1,3-benzenediamine as an orangeoil (2.3 g).

The above orange oil (2.3 g, 10 mmol) was treated with a solution of tin(II) chloride dihydrate (9.0 g, 40 mmol), 10 N hydrochloric acid (10mL), and ethanol (55 mL, absolute) at 40-50° C. for 18 h. The mixturewas worked up as described in Example 1 (exceptions: 20 wt % potassiumhydroxide solution (85 g) and hexane—ethyl acetate (1:1) were used inextraction). The crude oil that was purified by chromatography (silicagel) and kugelrohr distilled (115° C., 0.1 mm Hg) to giveN,N-diallyl-1,2,5-benzenetriamine, 2, as a yellow oil (0.75 g). ¹H NMR(CDCl₃) 6.58 (d, 1H), 6.41 (d, 1H), 6.33 (d of d, 1H), 5.80 (m, 2H),5.13 (m, 4H), 3.51 (d, 4H), 3.6 (bs) and 3.3 (bs).

EXAMPLE 3

Treatment of N-2-methylallyl-N-ethylamine with 2,4-dinitrofluorobenzeneas described in Example 1 gaveN-2-methylallyl-N-ethyl-2,4-dinitrobenzeneamine as a red oil (13.0 g).

Treatment of the red oil (13.0 g) from above with tin chloride asdescribed in Example 1 gaveN-2-methylallyl-N-ethyl-1,2,4-benzenetriamine, 3, as a yellow oil (bp100° C., 0.1 mm Hg). ¹H NMR (CDCl₃) 6.83 (d, 1H), 6.1 (m, 2H), 4.92 (s,1H), 4.83 (s, 1H), 4.05 (bs, 2H), 3.45 (bs, 2H), 3.31 (s, 2H), 2.79 (q,2H), 1.76 (s, 3H), 0.93 (t, 3H).

EXAMPLE 4

A mixture of 2,5-dinitrophenol (7.36 g, 40 mmol), allyl bromide (4.84 g,40 mmol), acetone (75 mL), 1-methylpyrrolidinone (3 mL) and potassiumcarbonate (11.0 g, 80 mmol) was heated to 50-60° C. for 22 h. Themixture was cooled to room temperature and filtered and the solid rinsedwith ethyl acetate. The filtrate was concentrated and recrystallizedfrom isopropanol-hexane (1:1) to give 2-allyloxy-1,4-dinitrobenzene asyellow crystals (8.36 g, mp 66.5-68° C.).

The above crystal (6.73 g, 0.03 mol) was dissolved in hot ethanol (60mL, absolute) and added to a solution of tin (II) chloride (45.5 g, 0.24mol), concentrated hydrochloric acid (36 mL), and ethanol (30 mL) at 40°C. The exothermic reaction was kept at 50° C. for 1 h and roomtemperature for 16 h. The mixture was diluted with water, basified with20 wt % potassium hydroxide (380 g), and extracted with hexane-ethylacetate (1:1). The combined extracts were washed with water twice anddried over magnesium sulfate. The extract was concentrated to an oil anddistilled (115-120° C., 0.1 mm Hg) to give2-allyloxy-1,4-benzenediamine, 4, as an oil. ¹H NMR (CDCl₃) 6.57 (d,1H), 6.26 (d, 1H), 6.19 (q, 1H), 6.06 (m, 1H), 5.39 (dq, 1H), 5.26 (dq,1H), 4.50 (dq, 2H), 3.37 (bs, 4H).

EXAMPLE 5

A mixture of 2,4-dinitrophenol (11.5 g, 80 wt %), 5-bromo-1-pentene(8.94 g, 0.06 mol), potassium carbonate (6.9 g, 0.05 mol) and1-methylpyrrolidinone (100 mL) was heated to 80-90° C. for 4 days.Further portions of 5-bromo-1-pentene were added after 2 days (4.3 g)and 3 days (3.23 g). The mixture was diluted with water and extractedwith hexane—ethyl acetate (1:2). The combined extracts were washed with10 wt % potassium hydroxide (100 mL) three times and three times withwater (100 mL) and then dried with magnesium sulfate. The solution wasconcentrated to give an oil. (13.4 g).

The oil (13.4 g, 0.053 mol) was treated with tin (II) chloride dihydrateas described in Example 1 (exceptions: reaction temperature was 40° C.and the extraction solvent was hexane-ethyl acetate, 1:1). The crude oilwas distilled to give a forerun (70-80° C., 0.1 mm Hg) and the desired4-(4′-pentenyloxy)-1,3-benzenediamine, 5, (135-140° C.) as an oil (4.62g).

EXAMPLE 6

A mixture of N-methylgeranylamine (1.35 g, about 90 wt %, 7.3 mmol),potassium carbonate (1.38 g, 10 mmol), 3-fluoro-4-nitroaniline (1.14 g,7.3 mmol) and 1-methylpyrrolidinone (10 mL) was stirred at 90-125° C.for 2.5 h. The mixture was diluted with water; extracted with ethylether; the extracts were washed twice with water and once with saturatedbrine solution; and extract was dried over magnesium sulfate.Concentration gave a orange oil that was purified by chromatography onsilica gel (hexane—ethyl acetate, 3.5:1) to give 1.3 g orange oil (59%).

The orange oil(1.3 g, 4.3 mmol) was treated with tin chloride dihydrateas described in example 1 (exceptions: reaction temperature was 30-34°C. for 2.5 h; and the extraction solvent was ethyl ether). The crude oilrecovered from the extraction was purified by chromatography on silicagel (hexane—ethyl acetate—tetrahydrofuran, 1:1:1) to giveN-methyl-N-geranyl-1,2,5-benzenetriamine, diamine 6, as an oil (0.96 g).

EXAMPLE 7

Treatment of 2,4-dinitrofluorobenzene with N-methyloleylamine isperformed as described in Example 1. The resulting dinitro compound istreated with tin (II) chloride dihydrate and purified by chromatographyto give the diamine 7.

EXAMPLE 8

Treatment of 2,4-dinitrofluorobenzene withN-methyl-3-methyl-3-butenylamine is performed as described in Example 1.The resulting dinitro compound is treated with tin (II) chloridedihydrate and purified by chromatography and distillation to give thediamine 8.

EXAMPLE 9

Treatment of 2,4-dinitrophenol with 8-bromo-2,6-dimethyl-2-octene isperformed as described in Example 5. The resulting dinitro compound istreated with tin (II) chloride dihydrate and purified by chromatographyto give the diamine 9.

EXAMPLE 10

Treatment of 3-fluoro-4-nitroaniline with N-methylcitronellylamine isperformed as described in Example 6. The resulting nitroamine is treatedwith tin (II) chloride dihydrate and purified by chromatography to givethe diamine 10.

EXAMPLE 11

Treatment of 3-fluoro-4-nitroaniline with N-methylfamesylamine isperformed as described in Example 6. The resulting nitroamine is treatedwith tin (II) chloride dihydrate and purified by chromatography to givethe diamine 11.

EXAMPLE 12

Treatment of 2,4-dinitrofluorobenzene with N-methylgeranylamine isperformed as described in Example 1. The resulting dinitro compound istreated with tin (II) chloride dihydrate and purified by chromatographyto give the diamine 12.

EXAMPLE 13

A mixture of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (428.3mg, 1.33 mmol), 2,5-diaminobenzonitrile, 13, (159.3 mg, 1.20 mmol),N,N-diallyl-1,2,4-benzenetriamine (diamine 1, 27.0 mg, 0.133 mmol) andγ-butyrolactone (2.44 g) was stirred at room temperature for 20.5 hunder a nitrogen atmosphere. The polyamic acid solution was diluted to 4wt % with γ-butyrolactone (12.0 g).

Two 0.9 inch by 1.2 inch by 1 millimeter thick soda lime glasssubstrates with transparent indium-tin-oxide (ITO) coatings (DCI, Inc.Lenexa, Kans. 66219) were spin-coated and cured with the polyimideformulation to give optical alignment layers. Spin coating was achievedby filtering the prepolymer solution through a 0.45 micron Teflon filtermembrane directly onto the surface of the clean ITO substrate. Thecoated substrates were spun at 2500 RPM for 1 minute to produce uniformthin films. The resultant thin films were cured under nitrogen for 0.25hr at 80° C. followed by 1 hr at 180° C.

FIG. 1 is a schematic of the experimental set-up used to expose thesubstrates. The laser beam of about 1 cm diameter from laser 1,polarized along direction 2, entered a polarizing rotator and beamsplitter combination 3 and, upon exiting, two polarization components 6and 7 separated as they propagated away from 3. The wavelength range ofthe laser was 300-336 nm. By adjusting the polarizing rotator in 3, theratio of optical power in 6 and 7 can be adjusted and, in this case, theratio was adjusted to be 1:6. The total power in 6 and 7 was 500 mW.Mirrors 5 reflected 6 and 7 through cylindrical lenses 8 and 9 withfocal lengths of 5 cm and 10 cm, respectively. After passing throughcylindrical lenses 8 and 9, 6 and 7 were focused into lines of about 1cm×0.2 cm onto the substrate(s) 10. The separation between the twoparallel focused lines was about 1.5 mm. As depicted in FIG. 2, thesubstrates 10 were scanned perpendicular to the focused lines. Since thefocused line lengths of about 1 cm was smaller than the desired exposurearea, after scanning one time, the substrates were stepped 1.5 mmperpendicular to the scan direction (along the focused lines). The stepand scan 11 were repeated until the entire substrate area was exposed.The scan speed for this exposure was 0.75 mm/s.

After exposure, the substrates were assembled with orthogonalorientation of the optically generated alignment direction. The cellthickness was about 4 microns. The cell was subsequently capillaryfilled with nematic liquid crystals suitable for active matrix liquidcrystal displays. As expected, the liquid crystals were observed toalign in a twisted nematic orientation when viewed between polarizers.Upon annealing the liquid crystal cell above the liquid crystalisotropic point (135° C. for 40 minutes), the uniformity of thealignment was observed to improve. The quality of the alignment for theannealed cell is described in Table 3.

Further trials (b, c and d) using scan speeds of 1.5, 3.0, and 6.0mm/sec are listed in Table 3. In a further trial (e) the polymersolution before spin-casting was diluted with a mixture ofγ-butyrolactone and 2-butoxyethanol to give a 3 wt % solution containing50 wt % 2-butoxyethanol.

In further trials f-j the 5 wt % polymer solution containing 52.6 wt %2-butoxyethanol was printed on the substrates using a Nissho PrintingCo. Angstromer SDR printer (Kenix Industries, Tempe, Ariz.). In trialsh-j the printed substrates were exposed with polarized light using alamp exposure unit similar to OptoAlign™ model E2-UV-600-SS-AA exposureunit (Elsicon, Inc., Wilmington, Del.).

EXAMPLE 14

A mixture of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (162.6mg, 0.505 mmol), 2,5-diaminobenzonitrile, 13, (53.7 mg, 0.403 mmol),N,N-diallyl-1,2,4-benzenetriamine (diamine 1, 20.5 mg, 0.101 mmol) andγ-butyrolactone (0.92 g) was stirred at room temperature for 22 h undera nitrogen atmosphere. The polyamic acid solution was diluted to 5 wt %with γ-butyrolactone (3.58 g), filtered through a 0.45 micron Teflonmembrane filter, and spin coated, cured and exposed to polarized lightas described in Example 13. The quality of the alignment for the celland VHR for various trial conditions is described in Table 3.

EXAMPLE 15

A mixture of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (215.3mg, 0.668 mmol), 2,5-diaminobenzonitrile, 13, (44.5 mg, 0.334 mmol),N,N-diallyl-1,2,4-benzenetriamine (diamine 1, 67.9 mg, 0.334 mmol) andγ-butyrolactone (1.33 g) was stirred at 60-70° C. for 20.5 h under anitrogen atmosphere. The polyamic acid solution was diluted to 5 wt %with γ-butyrolactone (4.90 g), filtered through a 0.45 micron Teflonmembrane filter. The solution was spin coated, cured and exposed topolarized light as described in Example 13. The quality of the alignmentfor the cell and VHR for various trial conditions is described in Table3.

EXAMPLE 16

A mixture of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (201.8mg, 0.626 mmol), N,N-diallyl-1,2,4-benzenetriamine (diamine 1, 127.2 mg,0.626 mmol) and γ-butyrolactone (1.31 g) was stirred at room temperaturefor 20.5 h under a nitrogen atmosphere. The solution was diluted to 5 wt% with γ-butyrolactone (4.94 g), filtered through a 0.45 micron Teflonmembrane filter, and spin coated, cured and exposed to polarized lightas described in Example 13. The quality of the alignment for the celland VHR for various trial conditions is described in Table 3.

EXAMPLE 17

A mixture of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (163.4mg, 0.507 mmol), N,N-diallyl-1,2,5-benzenetriamine (diamine 2, 20.6 mg,0.101 mmol), 2,5-diaminobenzonitrile, 13, (54.0 mg, 0.406 mmol), andγ-butyrolactone (0.94 g) was stirred at room temperature for 20.5 hunder a nitrogen atmosphere. The solution was diluted to 5 wt % withγ-butyrolactone (3.58 g), filtered through a 0.45 micron Teflon membranefilter, and spin coated, cured and exposed to polarized light asdescribed in Example 13. The quality of the alignment for the cell andVHR for various trial conditions is described in Table 3.

EXAMPLE 18

A mixture of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (226.9mg, 0.704 mmol), N,N-diallyl-1,2,5-benzenetriamine (diamine 2, 14.3 mg,0.070 mmol), 2,5-diaminobenzonitrile, 13, (84.4 mg, 0.634 mmol), andγ-butyrolactone (1.43 g) was stirred at room temperature for 20.5 hunder a nitrogen atmosphere. The solution was diluted to 4 wt % withγ-butyrolactone (6.38 g), filtered through a 0.45 micron Teflon membranefilter, and spin coated, cured and exposed to polarized light asdescribed in Example 13. The quality of the alignment for the cell andVHR for various trial conditions is described in Table 3.

EXAMPLE 19

A mixture of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (172.8mg, 0.536 mmol), N-2-methylallyl-N-ethyl-1,2,4-benzenetriamine, 3, (11.0mg, 0.054 mmol), 2,5-diaminobenzonitrile, 13, (64.3 mg, 0.483 mmol), andγ-butyrolactone (1.02 g) was stirred at room temperature for 21 h undera nitrogen atmosphere. The solution was diluted to 4 wt % withγ-butyrolactone (4.86 g), filtered through a 0.45 micron Teflon membranefilter, and spin coated, cured and exposed to polarized light asdescribed in Example 13. The quality of the alignment for the cell andVHR for various trial conditions is described in Table 3.

EXAMPLE 20

A mixture of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (290.5mg, 0.902 mmol), 2-allyloxy-1,4-benzenediamine, 4, (29.6 mg, 0.180mmol), 2,5-diaminobenzonitrile, 13, (96.0 mg, 0.721 mmol), andγ-butyrolactone (1.72 g) was stirred at room temperature for 21 h undera nitrogen atmosphere. The solution was diluted to 4 wt % withγ-butyrolactone (8.26 g), filtered through a 0.45 micron Teflon membranefilter, and spin coated, cured and exposed to polarized light asdescribed in Example 13. The quality of the alignment for the cell andVHR for various trial conditions is described in Table 3.

EXAMPLE 21

A mixture of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (259.0mg, 0.804 mmol), 4-(4′-pentenyloxy)-1,3-benzenediamine, 5, (30.9 mg,0.161 mmol), 2,5-diaminobenzonitrile, 13, (85.6 mg, 0.643 mmol), andγ-butyrolactone (1.48 g) was stirred at room temperature for 21 h undera nitrogen atmosphere. The solution was diluted to 4 wt % withγ-butyrolactone (7.54 g), filtered through a 0.45 micron Teflon membranefilter, and spin coated, cured and exposed to polarized light asdescribed in Example 13. The quality of the alignment for the cell andVHR for various trial conditions is described in Table 3.

EXAMPLE 22

A mixture of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (200.5mg, 0.622 mmol), N-methyl-N-geranyl-1,2,5-benzenetriamine, diamine 6,(17.0 mg, 0.062 mmol), 2,5-diaminobenzonitrile, 13, (74.6 mg, 0.560mmol), and γ-butyrolactone (1.11 g) was stirred at room temperature for23 h under a nitrogen atmosphere. The solution was diluted to 4 wt %with γ-butyrolactone (5.90 g), filtered through a 0.45 micron Teflonmembrane filter, and spin coated, cured and exposed to polarized lightas described in Example 13. The quality of the alignment for the celland VHR for various trial conditions is described in Table 3.

EXAMPLE 23

A mixture of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (175.2mg, 0.544 mmol), N-methyl-N-geranyl-1,2,5-benzenetriamine, diamine 6,(29.7 mg, 0.109 mmol), 2,5-diaminobenzonitrile, 13, (57.9 mg, 0.435mmol), and γ-butyrolactone (1.06 g) was stirred at room temperature for21.5 h under a nitrogen atmosphere. The solution was diluted to 4 wt %with γ-butyrolactone (5.25 g), filtered through a 0.45 micron Teflonmembrane filter, and spin coated, cured and exposed to polarized lightas described in Example 13. The quality of the alignment for the celland VHR for various trial conditions is described in Table 3.

EXAMPLE 24

A mixture of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (244.3mg, 0.758 mmol), 2-(trifluoromethyl)-1,4-benzenediamine, 14, (120 mg,0.682 mmol), N,N-diallyl-1,2,4-benzenetriamine, 1, (15.4 mg, 0.076 mmol)and γ-butyrolactone (1.56 g) was stirred at room temperature for 23.5 hunder a nitrogen atmosphere. The solution was diluted to 5 wt % withγ-butyrolactone (5.62 g), filtered through a 0.45 micron Teflon membranefilter, spin coated, cured and exposed to polarized light as describedin Example 13. The quality of the alignment for the cell and VHR forvarious trial conditions is described in Table 3.

EXAMPLE 25

A mixture of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (272.9mg, 0.847 mmol), 1,4-phenylenediamine, 17, (82.4 mg, 0.762 mmol),N,N-diallyl-1,2,4-benzenetriamine, 1, (17.2 mg, 0.085 mmol) and1-methylpyrollidone (1.54 g) was stirred at room temperature for 21 hunder a nitrogen atmosphere. The solution was diluted to 3 wt % with1-methylpyrrolidone (11.0 g), filtered through a 0.45 micron Teflonmembrane filter, spin coated, cured and exposed to polarized light asdescribed in Example 13. The quality of the alignment for the cell andVHR for various trial conditions is described in Table 3.

EXAMPLE 26 (Comparative)

A mixture of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (6.44 g),2,5-diaminobenzonitrile, 13, (2.66 g) and γ-butyrolactone (37.8 g) wasstirred at room temperature for 20 h under a nitrogen atmosphere. Thesolution was diluted to a 10 wt % solution with γ-butyrolactone (43.9 g)and filtered through a 0.45 micron Teflon membrane filter. The solutionwas diluted to 3 wt % solution and spin coated, cured and exposed topolarized light as described in Example 13. The quality of the alignmentfor the cell and VHR for various trial conditions is described in Table3. Comparison of Example 26 with Example 13, containing the crosslinkingdiamine 1, indicates that alignment quality and VHR are significantlyimproved in Example 13.

EXAMPLE 27 (Comparative)

A mixture of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (6.44 g),2-(trifluoromethyl)-1,4-benzenediamine, 14, (3.52 g) and γ-butyrolactone(40 g) was stirred at room temperature for 24 h under a nitrogenatmosphere. The solution was diluted to a 10 wt % solution withγ-butyrolactone (49.7 g) and filtered through a 0.45 micron Teflonmembrane filter. The solution was diluted to 3.5 wt % solution and spincoated, cured and exposed to polarized light as described in Example 13.The quality of the alignment for the cell and VHR for various trialconditions is described in Table 3. Comparison of Example 27 withExample 24, containing the crosslinking diamine 1, indicates thatalignment quality and VHR are significantly improved in Example 24.Thus, the crosslinking diamines give high quality alignment and high VHRat lower exposure energy levels than similar formulations not containingthe crosslinking diamines of the invention.

EXAMPLE 28

A mixture of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (6.44 g,20 mmol), ), 2,5-diaminobenzonitrile, 13, (2.334 g, 17.55 mmol),N,N-diallyl-1,2,4-benzenetriamine, 1, (0.396 g, 1.95 mmol) andγ-butyrolactone (36.5 g) was stirred at room temperature for 23.5 hunder a nitrogen atmosphere. The temperature was raised to 60° C. and4-(1H,1H-perfluorooctyloxy)benzenearnine, 15, (0.491 g, 1 mmol) inγ-butyrolactone (2.26 g) was added followed by continued heating for 21h. The solution was cooled and diluted to a 10 wt % solution withγ-butyrolactone (48.3 g) and filtered through a 0.45 micron Teflonmembrane filter. The solution was diluted to 4 wt % solution and spincoated, cured and exposed to polarized light as described in Example 13.The quality of the alignment for the cell and VHR for various trialconditions is described in Table 3. The cells exhibited a pre-tilt of 1and 1.5 degrees at 0.75 and 1.5 mm/sec exposure, respectively.

EXAMPLE 29

A mixture of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (6.44 g,20 mmol), ), 2,5-diaminobenzonitrile, 13, (2.334 g, 17.55 mmol),2-allyloxy-1,4-benzenediamine, 4, (0.320 g, 1.95 mmol) andγ-butyrolactone (36.7 g) was treated as described in Example 28 withfurther addition of 4-(1H,1H-perfluorooctyloxy)benzeneamine, 15, (0.491g, 1 mmol). The final solution was diluted to 4 wt % solution and spincoated, cured and exposed to polarized light as described in Example 13.The quality of the alignment for the cell and VHR for various trialconditions is described in Table 3. The cells exhibited a pre-tilt of0.6 and 1.2 degrees at 0.75 and 1.5 mm/sec exposure, respectively.

EXAMPLE 30

A mixture of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (6.44 g,20 mmol), ), 2,5-diarninobenzonitrile, 13, (2.127 g, 16 mmol),N,N-diallyl-1,2,5-benzenetriamine, 2, (0.406 g, 2.0 mmol), and diamine16 (0.552 g, 1.5 mmol) and γ-butyrolactone (37.9 g) was treated asdescribed in Example 28 with further addition of4-(1H,1H-perfluorooctyloxy)benzeneamine, 15, (0.491 g, 1 mmol). Thefinal solution was diluted to 4 wt % solution and spin coated, cured andexposed to polarized light as described in Example 13. The quality ofthe alignment for the cell and VHR for various trial conditions isdescribed in Table 3. The cells exhibited a pre-tilt of 0.6 and 1.2degrees at 0.75 and 1.5 mm/sec exposure, respectively.

EXAMPLE 31

A mixture of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (6.44 g,20 mmol), ), 2,5-diaminobenzonitrile, 13, (2.156 g, 16.2 mmol),N,N-diallyl-1,2,4-benzenetriamine, 1, (0.412 g, 2.03 mmol), and diamine16 (0.552 g, 1.5 mmol) and γ-butyrolactone (37.9 g) was treated asdescribed in Example 28 with further addition of4-(1H,1H-perfluorooctyloxy)benzeneamine, 15, (0.245 g, 0.5 mmol). Thefinal solution was diluted to 4 wt % solution and spin coated, cured andexposed to polarized light as described in Example 13. The quality ofthe alignment for the cell and VHR for various trial conditions isdescribed in Table 3. The cells exhibited a pre-tilt of 0.3 and 0.5degrees at 0.75 and 1.5 mm/sec exposure, respectively.

What is claimed is:
 1. A process for preparing an optical alignmentlayer for aligning liquid crystals comprising: preparing a layer ofpolymer selected from the group consisting of polyamic acid, polyamideester and polyimide, comprising anisotropically absorbing molecules, ona substrate, exposing said layer to polarized light; the polarized lighthaving a wavelength within the absorption band of said anisotropicallyabsorbing molecules; wherein the resulting exposed anisotropicallyabsorbing molecules induce alignment of a liquid crystal medium at anangle with respect to the major axis of the polarization of the incidentlight and along the surface of the optical alignment layer; wherein thepolymer is further characterized in having side chains selected from thegroup consisting of C₃-C₂₂ linear and branched hydrocarbon and partiallyfluorinated hydrocarbon chains, optionally substituted by one to twoheteroatoms selected from the group consisting of N, S, O and having oneto four carbon-carbon double bonds.